## Stream: Is there code for X?

### Topic: algebraic structures on lists

#### Hanting Zhang (Mar 17 2021 at 16:35):

Is there anything for index-wise addition on lists? Or a monoid structure? I couldn't find anything in mathlib and I wonder if it's because no one has done them yet, or because they were intentionally omitted.

#### Yakov Pechersky (Mar 17 2021 at 16:37):

what do you do for lists of different lengths?

#### Hanting Zhang (Mar 17 2021 at 16:44):

I'm not sure. I guess I would truncate to the smaller length, which would agree with list.map\2.